Conventionally, a fuel injection control device of an engine (in particular, a compression ignition engine) shown in FIG. 20 is known (for example, refer to Japanese Unexamined Patent Publication No. 2005-320870). In this device, in an interior of a body thereof, a needle 110 can communicate nozzle and suck chambers 120 and 130 with each other and shut them from each other, and defines the nozzle chamber 120 and a control chamber 140.
The nozzle chamber 120 is connected to a high pressure production part (having a fluid pressure pump and a common rail not shown) for producing a rail pressure Pc (high pressure) via a fuel supply passage 150. The suck chamber 130 is connected to a plurality of injection bores 160 facing a combustion chamber of the engine. The control chamber 140 is connected to the fuel supply passage 150 via a fuel inflow passage 170 and is connected to a fuel tank (not shown) via a fuel discharge passage 180. A control valve 190 for opening and closing the fuel discharge passage 180 is positioned in the fuel discharge passage 180.
The needle 110 is subject to a force by a pressure (the rail pressure Pc) in the nozzle chamber 120 in the opening direction (i.e. in the upward direction in FIG. 20) and is subject to a force by a pressure (a control pressure Ps) in the control chamber 140 and a spring force of a coil spring SP in the closing direction (i.e. in the downward direction in FIG. 20).
In this device, the control valve 190 is opened to open the needle 110 which is in a closed condition (i.e. a condition shown in FIG. 20, a lift amount=0) (i.e. to change the condition of the needle from the closed condition to an open condition (the lift amount>0)). Thereby, a fuel is discharged from the control chamber 140 to the fuel discharge passage 180, and then, the control pressure Ps decreases from the rail pressure Pc, and accordingly, the fuel flows into the control chamber 140 from the fuel supply passage 150 via the fuel inflow passage 170. As a result, the control pressure Ps decreases from the rail pressure Pc at a rate determined by a difference between outflow and inflow rates Qout and Qin (=Qout−Qin).
When the decreasing control pressure Ps reaches a “needle opening pressure” (i.e. the control pressure which may change the condition of the needle 110 from the closed condition to the open condition), the needle 110 opens (i.e. moves upwardly in FIG. 20), and as a result the fuel in the nozzle chamber 120 is injected from the injection bores 160 to the combustion chamber via the suck chamber 130. Thereafter, the needle 110 moves upwardly (i.e. moves in the upward direction in FIG. 20) against the spring force of the coil spring SP at a rate determined by a rate (=Qout−Qin) of decrease of the volume of the fuel in the control chamber 140. Accordingly, the fuel injection continues while the needle 110 is in the open condition.
On the other hand, the control valve 190 is closed to close the needle 110 which is in the open condition (i.e. to change the condition of the needle from the open condition to the closed condition). Thereby, the discharge of the fuel from the control chamber 140 via the fuel discharge passage 180 is ceased, while the flow of the fuel into the control chamber 140 via the fuel inflow passage 170 continues. As a result, the needle 110 moves downwardly (i.e. moves downwardly in FIG. 20) by means of the spring force of the coil spring SP at a rate determined by a rate (=Qin) of increase of the volume of the fuel in the control chamber 140. When the needle 110 is closed, the fuel injection is terminated. As explained here, the fuel injection is controlled by controlling the control valve 190 to control the control pressure Ps to regulate the lift amount of the needle 110.